Americans may paint themselves in increasingly bright shades of red and blue, but new research finds one thing that varies little across the nation: the liking for online pornography.

A new nationwide study (pdf) of anonymised credit-card receipts from a major online adult entertainment provider finds little variation in consumption between states.

"When it comes to adult entertainment, it seems people are more the same than different," says Benjamin Edelman at Harvard Business School.

However, there are some trends to be seen in the data. Those states that do consume the most porn tend to be more conservative and religious than states with lower levels of consumption, the study finds.

"Some of the people who are most outraged turn out to be consumers of the very things they claimed to be outraged by," Edelman says.

Political DivideEdelman spends part of his time helping companies such as Microsoft and AOL detect advertising fraud. Another consulting client runs dozens of adult websites, though he says he is not at liberty to identify the firm.

That company did, however, provide Edelman with roughly two years of credit card data from 2006 to 2008 that included a purchase date and each customer's postal code.

After controlling for differences in broadband internet access between states online porn tends to be a bandwidth hog and adjusting for population, he found a relatively small difference between states with the most adult purchases and those with the fewest.

The biggest consumer, Utah, averaged 5.47 adult content subscriptions per 1000 home broadband users; Montana bought the least with 1.92 per 1000. "The differences here are not so stark," Edelman says.

Number 10 on the list was West Virginia at 2.94 subscriptions per 1000, while number 41, Michigan, averaged 2.32.

Eight of the top 10 pornography consuming states gave their electoral votes to John McCain in last year's presidential election Florida and Hawaii were the exceptions. While six out of the lowest 10 favoured Barack Obama.

Old-Fashioned ValuesChurch-goers bought less online porn on Sundays a 1% increase in a postal code's religious attendance was associated with a 0.1% drop in subscriptions that day. However, expenditures on other days of the week brought them in line with the rest of the country, Edelman finds.

Residents of 27 states that passed laws banning gay marriages boasted 11% more porn subscribers than states that don't explicitly restrict gay marriage.

To get a better handle on other associations between social attitudes and pornography consumption, Edelman melded his data with a previous study on public attitudes toward religion.

States where a majority of residents agreed with the statement "I have old-fashioned values about family and marriage," bought 3.6 more subscriptions per thousand people than states where a majority disagreed. A similar difference emerged for the statement "AIDS might be God's punishment for immoral sexual behaviour."

"One natural hypothesis is something like repression: if you're told you can't have this, then you want it more," Edelman says.